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New York asteroid eclipse will be visible to millions

By Victoria Jaggard

Update, 20 March 2014&colon; Erigone is holding on to its secrets. Cloudy skies across New York state blocked out the view of the star Regulus during last night’s occultation by the asteroid, preventing us from teasing out more details about it. But IOTA says plenty more interesting occultations are on the horizon that will be easy to see with small telescopes.

Original article, published 18 March 2014

The people of New York City may be used to feeling at the centre of the world – and this week their city is at the nucleus of the latest asteroid hunt.

New Yorkers don’t need to panic&colon; the 72-kilometre-wide asteroid Erigone isn’t going to smash into the city. Instead, it is scheduled to eclipse Regulus – the brightest star in the constellation Leo – as seen from the Big Apple, plus a large part of upstate New York and parts of New Jersey, Connecticut, Ontario and Bermuda.

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Distant Erigone orbits the sun between Mars and Jupiter. If its predicted path is correct, the star will completely vanish for up to 14 seconds at about 0200 local time on 20 March. And the occultation should be visible to the naked eye, even through the bright lights of Manhattan.

Asteroid occultations are a common astronomy tool, though such events are usually only seen with a telescope and from dark corners of the globe. The International Occultation Timing Association (IOTA) is exploiting the fact that this one is potentially visible to millions of NYC citizens. Its vice president for planetary occultation services, Brad Timerson, gave us the scoop on what this week’s crossing will do for science, the possibility of seeing an asteroid “moon” and a peek into the life of an occultation timer.

What is the appeal of being a volunteer occultation timer? Seeing an occultation is pretty exciting. At that moment, you realise that the predictions made were accurate and that you have a chance to add to astronomical knowledge.

How often do you get to see an occultation?Asteroid occultations involving stars that are visible with naked eyes or amateur equipment occur several times each night. However, the paths are quite narrow and don’t always pass near many observers. I typically observe 15 to 20 events per year, of which three to four actually produce an occultation. The other events are “misses”, which are still quite useful.

Wait, how is not seeing anything helpful?After an occultation, we create a diagram of the [asteroid’s] path that includes parallel lines called chords. Each chord represents a slice of the asteroid as seen from different locations. If you are in the predicted path and don’t see the star vanish, your chord can help put constraints on the size of the asteroid. People elsewhere who do see the occultation will see the star blocked out for slightly different times. With enough chords, you can create a high-resolution outline of an asteroid that can constrain its size, shape and location.

What are you hoping to learn from the Regulus event?Regulus is a multi-star system, and the brightest star outshines its dim companion. It is possible that while the bright star is being blocked by the asteroid, we will get a glimpse of its companion star for a very brief time. That will help us learn its brightness and location in orbit around Regulus. Also, the asteroid Erigone may have its own satellites. Many asteroids that are large enough are known to have satellites, and they have been found before using occultations. It will not be an easy observation to find a satellite for Erigone, since we don’t know if one exists and therefore have no idea where to look. We can only say that it is likely to be within about 10 times the asteroid’s diameter and is likely to be pretty small.

So if I am in New York City, where should I go to see the occultation?You can be any place that has a clear view of the south-western skies. You are going to have to get away from buildings, in places like Central Park or the riverfront – any place with a clear view of the sky about half way up from the horizon.

How can I help with the science?We created a Regulus iPhone app that will record your time and your location using GPS. Then you just press a button when you see the star vanish and press it again when it reappears, and it will send us your data. We hope the high density of observers will give us a good look at the size and shape of this asteroid – although if you haven’t had a lot of practice, seeing a star vanish can take people by surprise, so there is a delay factor involved.

Will people throw occultation parties?One of the astronomy clubs in New York City is going to be having an observing party at a location along the river. That will be interesting for people to gather and see the event happen, but it is not that useful scientifically. You need people in lots of different locations to get enough chords. Occultation timers are kind of loners in that regard. We have to space ourselves out.